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RULE 2 PERMITS <br />This and other well data indicate that groundwater is draining from the dissected upper part of the <br />Williams Fork Formation and that there is not a single, continuous groundwater system on the property <br />above the elevation of Goodspring Creek. Test drilling on the mine site revealed that the limited amounts <br />of groundwater that exist on the site are usually perched on the highest impermeable bed. Continued <br />operation in the active pit during the permit term between 1981 and present has supported the conclusion <br />that little water exists in the sedimentary sequence and that where water is encountered it is limited both <br />vertically and laterally and under perched conditions. In addition, the excavation has been dry in the lower <br />seams where the sandstones show a greater lateral continuity and would be expected to contain more <br />water in storage than the upper seams. <br />Limited data are available to describe the hydraulic characteristics of the sandstones in the Williams Fork <br />and Iles Formations because most of the sandstones in the Williams Fork Formation contain only limited <br />quantities of groundwater. These sandstones have not been penetrated by water wells; therefore, no data <br />are available to describe their characteristics. However, Colowyo has completed two water wells into <br />deeper sandstones beneath the coal to be mined on the property. Aquifer tests completed on these two <br />wells yielded data that can be used to determine average hydraulic conductivities of these sandstones. <br />The Colowyo Taylor Creek No. 1 (see Map 10) is approximately 825 feet deep and produces 40 gpm on a <br />continuous basis. A 24-hour aquifer test was completed on the well and the drawdown data collected at <br />specific times during the test are shown in Figure 2.04.7-1. An analysis of the data by the Theis <br />nonequilibrium method reveals that the average transmissivity of the sandstone is 206 gallons per day per <br />foot (gdf) in the vicinity of the well. The average hydraulic conductivity was computed to be 3.4 gallons <br />per day per square foot. The storage coefficient presented on Figure 2.04.7-1 is 0.066, but should be <br />considered as a representation of storage conditions in the pumped well. There were no observation wells <br />available to calculate storage of the formation. The same condition was true for the Taylor Creek No. 3 <br />Well. <br />Taylor Creek No. 3 (see Map 10) was drilled to a depth of 2,284 feet to test the deep sandstones of the <br />Iles Formation. Three hundred feet of perforated casing was set between 1,335 feet and 2,284 feet. After <br />the well was completed, a 24-hour aquifer test was conducted. An analysis of the data indicated the <br />average transmissivity to be 40 gallons per day per foot. The average hydraulic conductivity was 0.13 <br />gallons per day per square foot. The drawdown data for Taylor Creek No. 3 is shown in Figure 2.04.7-2. <br />The results of the two tests indicate that the hydraulic conductivities of the sandstones below the coals to <br />be mined are low and variable. Because the hydraulic conductivities are low, little groundwater is <br />transmitted through the sandstones and discharged to the surface as springs or as base-flow in creeks. <br />Groundwater that is encountered on the property moves extremely slowly. <br />Recharge and Discharge <br />Aquifer tests conducted on the two Taylor Creek wells revealed low average hydraulic conductivities for <br />the sandstones. Because the hydraulic conductivity values are relatively low, recharge rates are also low. <br />Recharge to a groundwater system can be estimated by determining discharge from that groundwater <br />system. The U. S. Geological Survey (USGS) installed a continuous recording stream gage at the mouth <br />of Goodspring Creek. Analysis of the data reveals that the average groundwater discharge over the entire <br />Goodspring Basin is on the order of 0.2 to 0.35 inches per year. Since over a long period of time <br />groundwater recharge equals groundwater discharge, the recharge rates for the Taylor Creek Basin are <br />also on the order of 0.2 to 0.35 inches per year. These recharge rates are 1.0 to 1.5 percent of the annual <br />precipitation across the property. These are relatively low values, but the total runoff measured at the <br />USGS gage is only 2.6% of the annual precipitation. <br />Rule 2 Permits 2.04.7-4 Revision Date: 6/23/08 <br />Revision No.: MR-91